Wearing courses of stone and mastic on pavements

ABSTRACT

A hot mixture of stone and mastic is applied to the road foundation and compacted. The quantity and fluidity of the mastic is such that during and after the compacting, the mastic flows into the interstices between the stones forming the wearing course as a layer of mastic substantially free of voids, in which the stones are embedded, and with stone protruding from the upper surface thereof.

United States Patent 1191 Zichner Mar. 19, 1974 [5 WEARING COURSES 0F STONE AND 2.101.388 12/1937 Finley 94/23 MASTIC 0 PAVEMENTS 2.220.149 l1/1940 Finley..' 94/23 2,841,060 7/1958 Coppage.. 94/23 Inventor: Gerhard Zichner, Berglsch 3.091.543 5/1963 Rhodes.... 94/23 x Gladbach, Germany 3.291.628 12/1966 Jimenez... 94/23 X I 3.103.860 9/1963 Piquette 94/23 [73] Asslgnee: Srabag Cobgnebeum 3,02s 773 3/1962 McConnaughay 94/23 Germany [22] Filed: Aug. 3, 1971 Primary Examiner-Nile C. Byers. Jr.

Attorney, Agent, or Firm-Burgess, Dinklage & [21] Appl. No. 168,662 Sprung [30] Foreign Application Priority Data [5 7] ABSTRACT Aug. 10, 1970 Germany 2039627 A hot mixture of stone and mastic is applied to the road foundation and compacted. The quantity and flu- [52] US. Cl. 404/19, 404/72 idity of the mastic is such that during and after the [51] Int. Cl. E01c 11/24 compacting, the mastic flows into the interstices be- [58] Field of Search 94/23, 22; 404/19, 72 tween the stones forming the wearing course as a layer of mastic substantially free of voids, in which the [56] References Cited stones are embedded, and with stone protruding from UNITED STATES PATENTS the upper Surface thereof- 2.147,195 2/1939 Finley 94/23 17 Claims, 2 Drawing Figures a. 1A r. 54.,

(II I) I I n M INVENTOR GERHARD ZICHNER I BY BURGESS. DINKLAGE & SPRUNG ATTORNEYS WEARING COURSES OF STONE AND MASTIC ON PAVEMENTS BACKGROUND Pavements made of cobblestones, concrete or bituminous mineral mixtures are subjected to appreciable stress, especially on their surfaces, due to traffic and the weather. To extend their life they require the protection of wearing courses, which have to be renewed from time to time. These wear surfacings, which for reasons of economy must be kept as thin as possible, have the purpose of providing the pavement surface with the grip that is required for traffic safety and of protecting the underlying pavement against the penetration of moisture from rain and snow.

The commonly used thin, bituminous wear surfaces of a concrete type of composition, or those which consist of a course of mastic with gravel rolled into it, no longer suffice for the great stresses imposed by todays heavy traffic.

The conventional concrete-like bituminous wear surfaces have a dense mineral structure bonded with bitumen or cut bitumen, the quantity of the binding agent being such that the finished wearing course will contain 3 to 8 percent or as much as 10 percent by volume of air pockets or voids, depending 'on the nature of the binding agent. These wearing courses are laid by the hot paving method, using paving apparatus suitable for the purpose. The composition of these concrete-like bituminous wearing surfacings, however, provides neither a sufficient adhesion of the mineral particles to one another nor a sufficient adhesion of the wear surfacing to the underlying pavement. On account of the high percentage of voids in the wear surfacing, the binding agent forms only a relatively thin coating on each mineral particle, cementing the mineral grits together largely on naught but a point contact basis. This poor binding, of course, gives the concrete-like bituminous surfacing a poor resistance to wear. The stress produced by the vehicle tires easily pulls the mineral grits out of the surfacing, so that the surfacing is rapidly worn away, especially at the 'tire track areas, where it wears all the way down to the underlying pavement in a relatively short time. The deficient adhesion of the wear surfacing to the underlying pavement surface leads to peeling under the stresses of traffic, and this cannot be prevented even by priming with binding agents the pavement surface that is to be coated with the wear surfacing material. Lastly, the relatively great pore volume in the concrete-like bituminous wear surfacing permits the seepage of moisture from rain and snow into the surfacing and into the pavement beneath it, so that considerable damage may be done by the action of moisture.

In addition to this prior-art wearing course of asphalt concrete there is another one in use which consists of gravel with a mastic that serves as the binding agent. This wear surfacing material consists, according to the technical standards and guidelines for the construction of bituminous pavements published in the Federal Republic of Germany by The Federal Minister of Traffic, TV bit 6/60 (Gussdecken) No. 62, of a mastic coating on the underlying road pavement, in which crushed stone grave] is embedded. The mastic, according to No. 62.4 of the above-cited standards, consists of a mineral mixture composed of at least wt-% filler under 0.09

millimeter, 14 to 22 wt-% bitumen as binding agent, and the rest sand up to a grain size of 2 mm, the quantity of which is governed by the nature of the mineral substances and the anticipated fluidity of the mastic. The quantity ratio between mastic and grave] is to be equal to 1:1, according to TV bit 6/60 No. 62.232. The

laying of this wear surfacing has hitherto been performed in the following steps:

a. Application to the pavement surface of a course of 7 to 12 mm of hot liquid mastic. b. Uniform spreading of crushed stone gravel onto the hot coat of mastic. c. Rolling the gravel into the mastic coating. The preparation of the hot liquid mastic at the worksite requires the costly use of mastic heaters, while the application of the mastic to the pavement with swabs or scrapers or by means of drags requires expensive hand labor. At the same time,'the freshly applied thin coat of mastic is subject to such rapid cooling that the prior-art laying method canbe practiced only in the warm season of ,the year.

The spreading of the gravel, which is also performed by hand, does not assure the uniform distribution thereof, particularly when the gravel is provided with a thin coat of bitumen for better adhesion in the mastic layer, and this, of course, makes it more difficult to spread.

The rolling of the spread gravel must be performed immediately after the gravel is spread, on account of the rapidity with which the thin mastic layer cools. The use of special rubber multi-wheel rollers is required in order to assure the most uniform possible pressing of the gravel into the mastic layer. In spite of this difficult, expensive laying process, the wear surfacing of the prior art does not meet the requirements necessitated by highway traffic. Under the stresses of traffic it quickly becomes slick. This fault is due, according to my findings, on the one hand to the relatively high mastic content of 50 percent, and on the other hand to the poor bonding of the gravel grit within the mastic layer, caused by the paving method. The high mastic content considerably exceeds the volume of the interstitial spaces in the gravel component, and as a result the gravel is gradually forced completely into the mastic layer by the oncoming traffic. The deficient bonding of the gravel in the mastic layer is caused by the fact that the freshly laid mastic cools rapidly, thus forming a tough skin of low adhesivity on its surface; this tough skin envelops the gravel as the latter is forced into it and adheres poorly to it. Large amounts of this poorly bonded gravel ae pulled from the mastic layer by the tires of the oncoming vehicles and thrown aside. This substantially hastens the slickening of the surface of the wearing'course. At the same time the mastic loses the structural stability given it by the gravel, with the result that, especially in hot weather, it is displaced by the tires through pastic deformation, or it sticks to the tires and is torn up from the underlying pavement.

THE INVENTION The invention is addressed to the problem of improving the known method of laying wear surfacing materials consisting of gravel and mastic so as to simplify the process and eliminate the above-described disadvantages ofsuch wear surfacings.

This problem is solved in accordance with the invention in that a homogeneous hot mixture of gravel of a fineness of preferably not less than 2 mm with a mastic content that is smaller than the volume of the interstitial spaces in the gravel is applied to the underlying pavement surface, while the fluidity of the mastic is adjusted so that after application it settles down into the interstitial spaces in the gravel layer, and the mastic content is such that it flows together on the underlying road surface-to form a dense mastic layer from whose surface the crushed stone gravel protrudes.

Thus, the method of the invention involves making a wearing course on a roadway foundation by steps comprising forming a uniform hot mixture of stones and mastic; applying the mixture at an elevated temperature as a covering layer over the foundation; and compacting the mixture to form the wearing course as a layer of mastic bonded to the foundatiomThe layer of mastic is substantially free of voids, and the stones, covered with a film of mastic are embedded in the mastic, with some of the stones protruding from the upper surface of the layer. The quantity and fluidity of the mastic is such that during and after the compacting, the mastic flows into the interstices between the stones forming the wearing course as aforesaid, and in which the volume of the mastic is less than the interstitial volume of the stones.

The fluidity of the mastic that is needed in accordance with the selected gravel size or the size ofthe interstitial spaces therein is adjusted by means of its content of hot bitumen and/or filler.

In contrast to the prior-art paving method, the mastic layer that seals the pavement surface is produced by a partial settling out of the. mastic component from the hot mixtureafter it is laid. In thismanner the gravel is embedded into the mastic layer that is forming in such a manner that it lies on the pavement surface at the bottom, while at the top it partially protrudes from the surface of the mastic layer. The paving method ofthe invention thus creates a wearing course with a non-skid surface, whose .mastic layer protects theentire pavement surface and adheres tightly to same, but whose gravel grits are solidly supported on the underlying pavement. The hot mixing process, which also heatsthe gravel, brings about a complete wetting of the gravel with mastic, which is not adversely affected during the paving process owing to the hot state of the gravel. This results in a better bond between the gravel and the mastic, which experience shows, withstands even the severest traffic stresses. At the same time the consumption of mastic is substantially lower than in the wearing courses of the prior art, because the volume of the mastic is always less. than the interstitial volume of the gravel;

The hot mixtures suited to the performance of the process consist, in accordance with the invention, of more than 65 wt-% gravel preferably in sizes of 2-8 mm or 2-12 mm or 2-18 mm, and no more than 35 wt-% of mastic containing at least 20 wt-% of hot bitumen, and having a mixing temperature of 160 to 200 Cel-. sius. The crushed stone gravel for these hot mixtures is composed, in further development of the invention, of commercial sizessuch that, for thinner wear surfacings (e.g., to 3 cm.) the 2-5 mm and 5-8 mm gravel sizes; for medium wear surfacings (e.g.,3 to 4,5 cm.) the 2-5 mm, 5-8mm, and 8-12 mm sizes, or 5-8 and 8-12 mm sizes; and for the thicker wear surfacings (e.g. 4,5 and more cm.) the 2-5mm, 5-8 mm, 8-12 mm and 12-18 mm sizes, are preferably intermixed. These gravel size on the one hand, and on the other hand a good interfitting of the individual pieces or gravel is assured.

The high gravel content in these hot mixtures, of more than 65 wt-%, results in a self-supporting gravel structure resting firmly on the underlying pavement surface, and this structure undergoes no lateral displacement of the gravel particles even under great stress from motor vehicle tires. The above-stated gravel sizes assure sufficiently large interstices in the gravel structure, through which the mastic can with certainty settle down onto the underlying pavement surface after the hot mixture is deposited, in order to form the mastic coating that seals the said pavement surface. The mastic content of no more than 35 percent by weight assures that, after the settling of the mastic has ended, the gravel grits will protrude sufficiently far up from the surface of mastic layer, say by one-third to one-half the size of the grits, with its lower portion embedded sufficiently firmly in the said layer. This gives the wearing course the desired rough,skid-resistant surface plus an optimum tight bonding of the gravel grits in the mastic layer so that they cannot be pulled out of the mastic layer by the tires of the oncoming motor vehicles.

The stone content of the stone-mastic mixture can be 65-80,.preferably to wt-% and the mastic can be 20-35, preferably 25-30 wt-% of the mixture. Desirably at least 20 percent; preferably 23-28 percent of the mastic is bitumen. A preferred composition is 70 wt-% stone, 8 wt-% bitumen (in the mastic) 12 wt-% filler (in the mastic), based on total weight of stone plus mastic.

The high hot bitumen content in the mastic used ih the hot mixtures assures thatthe mastic will settle out of the gravel and form the continuous mastic coating on the underlying pavement, even in cool weather.

The consistency of the hot mixtures according to the invention enables them to be transported to the worksite in ordinary trucks without any fear of appreciable separation of the components in transit. In the case of particularly long hauls and of high air temperatures, premature separation can be prevented by the addition of stabilizing agents made of ground rubber or plastic, fibers, ground clay or shale, or the like.

The consistency of the hot mixtures according to the invention furthermore enables them to be laid with normal, conventional paving machines for bituminous surfacing materials, in a single procedure. This assures the precise maintenance of a uniform thickness in the relatively thin wear surfacing without the need for expensive manual labor. The installed wearing course can be compacted with any conventional type of roller used in the art for similarpurposes.

The expense involved in equipment and the amount of time required for the laying of the wearing course is thus appreciably less than in the case of the known laying method; in particular, no manual labor is necessary.

The hot mixture, due to its high content of gravel which is heated to the laying temperature while it is being mixed with the mastic, has a high total heat, so that dependence on the weather is far slighter than it is in the prior-art process.

EMBODIMENTS An example of the embodiment of the invention is shown in the drawing in two characteristic phases of the process.

F IG. 1 is a cross section of the wearing course immediately after it has been laid;

FIG. 2 is the same cross section of the finished wearing course.

In the uniform, hot mixture of gravel 2 and mastic 3 applied to a roadway surface 1, as shown in FIG. 1, there is a thick coating of mastic enveloping the gravel grits.

Immediately after the application of the mixture to the roadway surface, the mastic begins slowly to run down from the gravel and, bit by bit, to flow together on the roadway surface to form a continuous mastic coating 4, leaving the gravel to protrude from its surface, because the volume of the mastic is smaller than the interstitial volume of the gravel. At the same time, the gravel settles, with a thin film of mastic between the particles, directly onto the roadway surface 1. This is made possible by the relatively large interstices in the structure formed by the gravel and is sustained by the high heat content of the gravel itself, thereby assuring the formation of the mastic seal coat even in cool weather. The process can be delayed as required, e.g. in hot weather, by means of the above-described additives, to such an extent that no intolerable separation of the components will occur during transportation of the mixture tothe worksite on the one hand, and on the other hand the settling of the mastic from the gravel after the surfacing is laid will be assured. The bonding of the gravel 2 in the mastic coating 4 is particularly good on account of the previous hot mixing process, as is also the bond between the mastic'layer and the roadway surface 1 which is to be protected or roughened. A thin, tight seal coating of mastic remains on the part of the gravel grits that protrude from the mastic layer. The adherence of the mastic sealing layer to the roadway surface can be improved in known manner by the preliminary spraying of hot bitumen or road tar onto the roadway surface to form a thin film of, e.g., about 0.2 to 0.5 mm.

The hot mixture can be 65 wt-% stone, and 35 wt-% mastic 20 which is 20% bitumen. The stone can be an admixture of the two stone size distributions 2-5 mm,

' and 58 mm, with the 2-5 mm size distribution being e.g. 25 wt-% and the 5-8 mm stone size distribution being e.g. 75 wt-% of the total weight of the stone. The mixing temperature can be 170 to 200 C. The mixture can be formed by the procedure and with the equipment known in the art for the hot paving method. The resulting mixture can be applied to a road foundation at an ambient temperature up to 20C, without the use of stabilizers to prevent separation, if applied within e.g. 1 hours of the production thereof.

The wearing courses of the invention are substantially free of voids, by which is meant, contain less than rounded to rounded to mrn rnrnX0.04 64ths of inch l6ths of inch All in all, the method taught by the invention and the procedures made possible thereby provide a wear surfacing characterized by high resistance to abrasion. long-lasting surface roughness, and reliable adhesion to the road surface.

What is claimed:

1. Method of making wearing course on a roadway foundation resistant to lateral displacement in response to the stress of traffic, comprising:

a. forming a uniform hot mixture consisting essentially of stones and mastic, the stones being more than 65 wt-%, the mastic being less than 35 wt-%, of the stone and mastic mixture, the stone being not less than about 2 mm, the mastic being at least 20 wt-% bitumen, the stone size being distributed within the range of 2-18 mm, applying the mixture at an elevated temperature as a covering layer over the foundation, and

compacting the mixture to form the wearing course as a layer of mastic bonded to the foundation, substantially free of voids in which the stones covered with a film of mastic are embedded with stones protruding from the upper surface thereof, the quantity and fluidity of the mastic and size distribution of the stone being such that during and after said compacting, the mastic flows into the interstices between the stones forming the wearing course as aforesaid and in which the volume of the mastic is less than the interstitial volume of the stones.

2. Method according to claim 1, the stones being crushed stones.

3. Method according to claim 1, the stones being a distribution in one of the ranges 2-8 mm, 2-12 mm, and 2-18 mm.

4. Method according to claim 1, substantially all of the stones being a mixture of stone size distributions 2-5 mm and 5-.-8 mm.

the stones being a mixture of stone size distributions 2-5mm and 58 mm and 8-12 mm, or 5-8 mm and 8-12 mm.

6. Method according to claim 1, substantially all of the stones being a mixture of stone size distributions 2-5 mm and 58 mm and 8-12 mm and 12-18 mm, or 58 mm and 8-12 mm and 12-18 mm, or 8-12 mm and 12-18 mm.

7. Method according to claim 4, the wt-% of the stone size distributions increasing as the stone size distribution becomes coarser.

8. Method according to claim 5, the wt-% of the stone size distributions increasing as the stone size distribution becomes coarser.

9. Method according to claim 6, the wt-% of the stone size distributions increasing as the stone size distribution becomes coarser.

10. Method according to claim 1, and including in the hot mixture a stabilizing agent to prevent separation of the mixture before said application thereof.

11. A road comprising a foundation and a wearing course bonded to the foundation, the wearing course comprising a layer of mastic in which stones covered 5. Method according to claim 1, substantially all of' with a film of mastic are embedded, bonded to the foundation, substantially free of voids, stones protruding from the outwardly disposed surface of the wearing course, the stones being not less than about 2 mm and being more than 65 wt-% of the stone and mastic, the mastic being less than 35 wt-% of the stone and mastic layer, the mastic being at least 20 wt-% bitumen; the stone size being'distributed within the range of 2-18 12. A composition for production of a wearing course on a road foundation, spreadable to form a layer over the foundation which is compactable to form the wearing course as a layer of mastic in which stones covered with a film of mastic are embedded, bonded to the foundation, substantially free of voids, and with stones protruding from the outwardly disposed surface thereof, consisting essentially of a uniform hot mixture of stones and mastic in which the stones are not less than about 2 mm and are at least 65% by weight of the stone and mastic mixture, the mastic being less than 35 wt-% of the stone and mastic mixture, the mastic being at least 20 wt-% bitumen, the stone size being distributed within the range of 2-18 mm.

13. Road according to claim 11, the stones being 70-75 wt. the mastic being 25-30 wt.%, of the stones plus mastic, the mastic being 23-28 wt-% bitumen.

14. Composition according to claim 12, the stones being 70-75 wt.%, the mastic being 25-35 wt.%, of the stones plus mastic, the mastic containing bitumen in an amount such that 23-28 of the percentage points of the mastic are bitumen.

. 15.Method according to claim 1, the stones being -80 wt.%, the mastic being 20-35 wt.%, of the stone plus mastic.

16. Method according to claim 1, the stones being -75 wt.%, the mastic being 25-30 wt.%, of the stone plus mastic.

17. Method according to claim 16, the mastic containing bitumen in an amount of 23-28 wt%. 

1. Method of making wearing course on a roadway foundation resistant to lateral displacement in response to the stress of traffic, comprising: a. forming a uniform hot mixture consisting essentially of stones and mastic, the stones being more than 65 wt-%, the mastic being less than 35 wt-%, of the stone and mastic mixture, the stone being not less than about 2 mm, the mastic being at least 20 wt-% bitumen, the stone size being distributed within the range of 2-18 mm, b. applying the mixture at an elevated temperature as a covering layer over the foundation, and c. compacting the mixture to form the wearing course as a layer of mastic bonded to the foundation, substantially free of voids in which the stones covered with a film of mastic are embedded with stones protruding from the upper surface thereof, the quantIty and fluidity of the mastic and size distribution of the stone being such that during and after said compacting, the mastic flows into the interstices between the stones forming the wearing course as aforesaid and in which the volume of the mastic is less than the interstitial volume of the stones.
 2. Method according to claim 1, the stones being crushed stones.
 3. Method according to claim 1, the stones being a distribution in one of the ranges 2-8 mm, 2-12 mm, and 2-18 mm.
 4. Method according to claim 1, substantially all of the stones being a mixture of stone size distributions 2-5 mm and 5-8 mm.
 5. Method according to claim 1, substantially all of the stones being a mixture of stone size distributions 2-5mm and 5-8 mm and 8-12 mm, or 5-8 mm and 8-12 mm.
 6. Method according to claim 1, substantially all of the stones being a mixture of stone size distributions 2-5 mm and 5-8 mm and 8-12 mm and 12-18 mm, or 5-8 mm and 8-12 mm and 12-18 mm, or 8-12 mm and 12-18 mm.
 7. Method according to claim 4, the wt-% of the stone size distributions increasing as the stone size distribution becomes coarser.
 8. Method according to claim 5, the wt-% of the stone size distributions increasing as the stone size distribution becomes coarser.
 9. Method according to claim 6, the wt-% of the stone size distributions increasing as the stone size distribution becomes coarser.
 10. Method according to claim 1, and including in the hot mixture a stabilizing agent to prevent separation of the mixture before said application thereof.
 11. A road comprising a foundation and a wearing course bonded to the foundation, the wearing course comprising a layer of mastic in which stones covered with a film of mastic are embedded, bonded to the foundation, substantially free of voids, stones protruding from the outwardly disposed surface of the wearing course, the stones being not less than about 2 mm and being more than 65 wt-% of the stone and mastic, the mastic being less than 35 wt-% of the stone and mastic layer, the mastic being at least 20 wt-% bitumen, the stone size being distributed within the range of 2-18 mm.
 12. A composition for production of a wearing course on a road foundation, spreadable to form a layer over the foundation which is compactable to form the wearing course as a layer of mastic in which stones covered with a film of mastic are embedded, bonded to the foundation, substantially free of voids, and with stones protruding from the outwardly disposed surface thereof, consisting essentially of a uniform hot mixture of stones and mastic in which the stones are not less than about 2 mm and are at least 65% by weight of the stone and mastic mixture, the mastic being less than 35 wt-% of the stone and mastic mixture, the mastic being at least 20 wt-% bitumen, the stone size being distributed within the range of 2-18 mm.
 13. Road according to claim 11, the stones being 70-75 wt. %, the mastic being 25-30 wt.%, of the stones plus mastic, the mastic being 23-28 wt-% bitumen.
 14. Composition according to claim 12, the stones being 70-75 wt.%, the mastic being 25-35 wt.%, of the stones plus mastic, the mastic containing bitumen in an amount such that 23-28 of the percentage points of the mastic are bitumen.
 15. Method according to claim 1, the stones being 65-80 wt.%, the mastic being 20-35 wt.%, of the stone plus mastic.
 16. Method according to claim 1, the stones being 70-75 wt.%, the mastic being 25-30 wt.%, of the stone plus mastic.
 17. Method according to claim 16, the mastic containing bitumen in an amount of 23-28 wt%. 